1. Field of the Invention
The invention relates to a plasma producer with a holder, e.g. for a welding device.
2. Description of the Prior Art
In plasma producers of known devices the cathode and anode are usually connected to connecting cables wish clamping joints and mechanically connected with one another by way of respective range spacers which also determine the chamber through which a respective gas is supplied to the arc burning between the anode and cathode.
As a result of the unavoidable wear of the cathode, it must be reworked after a certain number of working hours. For this purpose it is necessary to disassemble the plasma producer and to re-grind the cathode. Then it is necessary to adjust the cathode with respect to the anode with extreme precision again in order to be able to perform the intended working of a work piece such as the application of a weld seam or the application of a metal layer. This adjusting work requires a considerable amount of time and causes considerable standstill periods of the tool and thus production losses.
For this reason laser or electron-beam devices are used in mass production for different tasks, e.g. for welding or cutting, although they are considerably more expensive in production than devices that work with plasma, e.g. welding devices, and the required preparation for the work pieces to be welded is considerably higher since laser and electron beams can produce heat only by absorption, but do not radiate any heat themselves as is the case with plasma.
From U.S. Pat. No. 5,258,599 A and EP 0 079 019 A1 devices are known for example in which plasma producers are provided which work with consumable cathodes and in which the anodes plus holders are arranged as a module and can be handled together. This module can be removed from a holder which also comprises the fixing device or guide means for the consumable cathode.
In these known solutions an axial supply of the cathode and also the supply with gas is provided and the connection of the electric power supply also occurs in the axial direction of the chamber.
This leads to the disadvantage, however, that the plasma producer has a very large overall length. As the plasma producer is usually clamped in a receptacle of a welding robot at its end zone which is averted from the nozzle orifice, there will be respectively large imprecisions in the guidance of the orifice of the nozzle which is decisive for the success of the working and the reproduceability as a result of the unavoidable tolerances, in particular after changing the module.
Moreover, for currents of more than 1000 A plasma producers have very large diameters and thus have very large masses. Furthermore, cross sections of the paths of the current which are required for such currents can hardly be achieved, so that it is necessary to work with respectively high current densities, which leads to a respective heating of the current-carrying parts.
The close distance of the current-bearing parts, which is unavoidable in such axially divisible plasma producers in the case of slender designs, leads in the case of high ignition voltages which are required in particular in case of an operation with helium gas to internal arc-overs and thus to ignition failures.